A PWB often includes an RF filter, such as a high frequency (HF) filter. Because the performance of some RF filters depends on the geometry of the filter layout on the PWB, the performance of such filters may be impacted by the tolerances used to manufacture the filter. I.e., tight tolerances generally increase the likelihood that the manufactured RF filter will meet a specified RF response. For example, a manufacturer may use a tight etching tolerance to create a PWB and the RF filter thereon. However, it is generally more expensive to manufacture PWB's using tight tolerances.
Conversely, it may be less expensive to manufacture a PWB with a looser or more variable tolerance. However, use of such looser tolerances may tend to increase the number of PWBs that do not meet specified performance standards (i.e., again increase the number of non-compliant PWBs). In some instances, such non-compliant PWBs are scrapped, thus effectively reducing the total yield of useful PWBs. In other instances, these non-compliant PWBs can be tuned, or reworked, to bring them into compliance. However, such tuning or reworking of the PWB tends to be expensive and the manufacturer may not realize much of a cost savings over just manufacturing a tighter tolerance PWB.
In regards to tuning, at high frequencies, which is generally considered to comprise frequencies above 500 MHz, a filter's performance may be tuned, for example, by mechanically changing a filter cavity with a screw or by moving one of the surfaces. Even though this type of tuning may shift the RF response, it may compromise the in-band return loss and out-band rejection because the phase and impedance have not been scaled properly. Another method of tuning RF filters is to physically change the size of the resonators by soldering tuning pads, wire bonding to tuning pads, and/or laser trimming. These methods are generally labor intensive and/or require special processes such as wire bonding or laser trimming.
Therefore, a need exists for an improved method of tuning an RF filter, for example, in a PWB. Furthermore, a need also exists for an improved method of reworking a non-compliant PWB.